Science - water filter

 Water from lakes and rivers carries bacteria and bugs as well as sediment. While filtered water isn't safe to drink it can be made cleaner by filtering. 

I used cotton wool, charcoal to remove contaminants, sand because the small pores trap many tiny organisms, and gravel and pebbles in increasingly smaller particles. 

This went quite badly and we somehow ended up with dirtier water from the river Nidd but I understand the process.